<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style type="text/css">
	.box1{background:red; height:200px;}
	<!-- absolute需要有已经定位的父元素，那么它的原始位置依旧保持在原来的位置（参照基准） -->
	.box2{background:green; height:100px;position:absolute;}
	.box3{background:blue; height:200px;}
	.box{position:relative;height:60px; background:yellow;}
</style>
</head>

<body>
	<div class="box1">box1</div>
   	<div class="box">
      	<div class="box2">box2</div>
      </div>
   <div class="box3">box3</div>
</body>
</html>
